BOSTON — As game-winning RBI go, it wasn’t the most exciting Sean Casey has ever had.

But that’s not to say his bases-loaded walk in a four-run eighth inning that capped the Red Sox’ rally from a 5-0 deficit yesterday afternoon against the Rangers wasn’t satisfying.

It was a comeback that showed Boston’s talent and tenacity, a rousing finish that displayed to a delighted, sun-drenched sellout crowd the Sox’ winning combination of timely hitting, speed on the bases, and the ability to treat not just every at-bat, but every pitch, as if the World Series depended on it.

“One thing that’s impressed me about this club,” said Casey, who signed with the Sox as a free agent in February, “is the way guys fight to get on base. There aren’t many wasted at-bats. I’ve quickly come to realize that this offense can strike at any time. We’ve got so many big bats, so many guys who can get on base. Things can happen in an instant.

“Nobody here ever thinks the game is over. Even though we were five runs down, we kept grinding. I’ve been on teams where, when they got down, they were waiting to lose. This team expects to win.”

And they usually do.

The Red Sox have won 13 times in 20 games this season and have come from behind in 8 of those victories, including 5 of their last 6. They’ve now won four in a row, and eight of their last nine.

“We stay positive,” Casey said. “Instead of thinking negatively, we’re thinking: ‘Let’s get some guys on base and get something going.’ ”

The problem for the Sox, through the first six innings, was not getting guys on base — it was getting them home. They left the bases loaded in both the fifth and sixth, bringing their total of stranded runners to 10 at that point.

Boston finally broke through with two runs in the seventh, but, with two outs and nobody on in the eighth, it seemed as if all the Sox had done was avert a shutout, not defeat.

“Once again, we had them where we wanted them,” said Texas manager Ron Washington, who’d seen Boston come up with three runs in the eighth inning Saturday night to wipe out the Rangers’ 3-2 lead. “We’ve had them beat twice now, and we let them get away. We’ve got to learn how to put games away.”

The Red Sox have learned that it’s as much about attitude as it is about aptitude.

“You keep playing,” Boston manager Terry Francona said, “because, every once in a while, if you’ve got a good enough team — like we feel we do — you win some of those. If you stop playing, or you feel sorry for yourself, you don’t. There’s something to be said for just plugging away.”

That’s what the Sox did yesterday and, as Francona said: “Some good things happened. Actually, some great things happened.”

What happened in the eighth was that Jacoby Ellsbury, who’d popped out with the bases loaded two innings earlier, got things started with a single. Fellow rookie Jed Lowrie, playing in just his fifth major-league game, followed with a run-scoring double, and then came home when David Ortiz hustled down the first-base line to beat out a sharp grounder that Texas second baseman Ian Kinsler had fielded with a diving stab in right field.

It was a determined effort by Ortiz, and a heads-up play by Lowrie, who went unnoticed by Rangers first baseman Ben Broussard.

“You have to be aware,” Washington said, “that you have a runner at second. You just can’t let him cross the dish. If Broussard realized they called David safe, and there’s a runner at second, he has to come back to the plate. We’d have blown that guy up at home.”

Instead, the Rangers wound up blowing their five-run lead, as Dustin Pedroia, coming off the bench as a pinch-hitter, drilled a game-tying double, and Casey, after falling behind in the count, 1-2, worked Rangers reliever C.J. Wilson for a bases-loaded, game-winning walk.

A career .302 hitter, Casey is comfortable at the plate in pressure situations. In the 2006 World Series with the Tigers, he was 9-for-17 — a dazzling .529 average — with two homers. Despite his hitting heroics, Detroit lost to the Cardinals in five games.

“I’ve been in those situations a lot,” he said. “You’ve got to stay relaxed. The times I’ve gone up there all geared up to do something, I haven’t had such great at-bats. I’ve never felt nervous hitting with two strikes. I was just trying to get a pitch I could hit, trying to make (Wilson) work. He missed up and in, then down and away. I got the count to 3-2, and he threw one high.”

The Red Sox are riding high after pulling out yet another come-from-behind win.

“Any time you come back and win like that,” Casey said, “it brings you together. It’s exciting. It brings a sense of unity to the team.”

The chance to win a World Series is why Casey, who spent the first eight years of his career in Cincinnati, signed with the Sox.

“To play in front of this crowd, with these guys, is pretty awesome,” Casey said. “It doesn’t get much better than coming back to win like that.”

jdonalds@projo.com